Gas-generating devices



Sept. 6, 1966 B. SILVER 3,270,502

GAS-GENERATING DEVICES Filed Sept. 30, 1964 gig. 1

INVENTOR BERNARD SILVER AGENT United States Patent 3,270,502 GAS-GENERATING DEVICES Bernard Silver, Alexandria, Va., assignor to Atlantic Research Corporation, Fairfax County, Va., a corporation of Virginia Filed Sept. 30, 1964, Ser. No. 400,479 11 Claims. (Cl. 60--35.6)

This invention relates to ga s-generating devices and to the gas-generating elements within these devices.

As used herein, the terminology gas-generating element and element designates that solid component within the device which actually contains the material that takes part in the gas-producing reaction. Normally this reaction is a combustion process although other gas-producing reactions such as heat-initiated autodecompositions, catalytically induced decompositions, and the like also are used.

Gas generating devices are used extensively, the most well-known application being the rocket motor. Other uses include powering small turbines on large space boosters, pressurizing liquids in liquid-propellant propulsion systems, and the like.

For brevity, the discussion herein is directed to devices producing hot gases as a result of a combustion process. The features of the present inventions are, however, applicable to gas-generating devices employing decomposition reactions and the like.

Many gas-generating devices are loaded by a cartridge loading technique wherein the element is fabricated outside of the device and thereafter inserted into the combustion chamber as a single unit. This technique makes it necessary for the cross-sectional dimensions of the chamber to be slightly larger than those of the element to facilitate loading. Consequently there is a space between at least a portion of the exterior lateral surface of the element and the chamber wall. For this reason, cartridge-loaded elements usually comprise an inhibitor to prevent burning along the lateral surface.

There are several possible causes for failure in cartridge-loaded gas-generating devices. The length of the element :and chamber should not permit any substantial endwise movement. Otherwise, the element may move against the end of the chamber with sufficient force to splinter or fracture. Due to thermal expansion of the element and chamber walls, it is difficult to limit movement over a wide range of temperatures since their coefiicients of expansion are usually very different. Combustion gases can enter the space between the element and the chamber wall causing overheating of the wall unless it is insulated or made sufficiently thick to withstand the heat. As thick walls and insulation present weight problems, expensive, heat-resistant alloys are used to fabricate the walls. Hot gases tend to elevate the temperature of the grain producing an increase in burning rate. In addition, the heat can cause the inhibitor coating to soften, weaken, or burn. This in turn may lead to puncture of the coating or its separation from the burning g-rain. Hot gases also may penetrate small holes in the inhibitor and ignite the grain at additional points ahead of the intended burning surface causing erratic burning and/ or explosion.

It is an object of the present invention to provide improved gas-generating devices comprising a gas-generating element having resilient members attached thereto. Another object is to provide a gas-generating device in which the gas-generating element provides a gas-seal between the element and the chamber wall to prevent gas from entering the space between the lateral surface of the element and the walls of the combustion chamber. A further object is to provide an improved gas-generating element which remains substantially free from movement along its longitudinal axis over a wide temperature range. A still further object is to provide an improved gas-generating element having a resilient member at each end as an essential part of the element. The manner in which these as well as other objects can be accomplished will become apparent from the following detailed discussion wherein:

FIGURE 1 is an exploded sectional view of one embodiment of a gas-generating device according to this invention;

FIGURE 2 is a longitudinal cross-section of the assembled device of FIGURE 1;

FIGURE 3 is an enlarged fragmentary view of the assembled device of FIGURE 2 showing the relationship of the casing, nozzle insert, and gas-generating element;

FIGURE 4 is an end view partially cut-away taken along line Z2 of FIGURE 2; and

FIGURES 5 and 6 are perspective views partially in section of variations in configuration for the resilient members used in making the gas-generating elements of the present invention.

Basically, this invention encompasses an improved gas-generating element and a gas-generating device employing the element. The element comprises four basic components: a solid gas-generating grain, an inhibitor coating, and two heat-resistant, resilient members. A member it attached to one end of the inhibited grain and normally adheres to both the exposed end surfaces of the coating and the grain. At least one of the resilient members has a passage to permit gas flow therethrough.

The gas-generating device of the invention comprises a heat-resistant casing or ho-u-sing forming a combustion chamber and having a restricted exhaust port for venting the gases. The longitudinal chamber axis and that of the port will normally be substantially aligned. The end portion of the casing surrounding the port for-ms a rear chamber wall against which one of the resilient members of the gas-generating element can abut.

The element is positioned in the combustion chamber with a member having a passage therethrough abutting against the rear chamber wall and the other member abutting against the forward chamber wall. Preferably the resilient members are compressed against the walls to maintain the element in a substantially stationary position and to provide a gas-tight seal between the resilient member and the wall.

A clearer understanding of the invention is possible by referring to the drawings wherein like numerals indicate like parts.

FIGURES 1. and 2 show a rocket motor 10 representing one embodiment of a gas-generator according to the present invention. Nozzle 12 is provided with a nozzle flange 16 which extends inwardly into and around the circumference of nozzle passage 14. Nozzle insert 18 having aperture 22 fits into the nozzle passage with one end 20 abutting the nozzle flange.

The casing is provided with a restricted annular exhaust port 28 at the rearward end of the cylindrical combustion chamber 30. Closure 26 forms the forward wall 27 of the chamber. The diameter d of the port is less than the diameter D of the chamber, thus forming rear wall 32.

Element 34 comprises (1) the grain 36 having internal perforation 38 therethrough, (2) inhibitor coating 40 adhering to the lateral surface 42 of the grain, and (3) two heat-resistant resilient members 44 and 46 with passage 48 therethrough attached to the ends of the inhibited grain. The surface 50 on the exposed side of the member, that is, the side opposite the one adhering to the grain, has a continuous groove 52 spaced from the center and the outer edge 54 of the member.

The motor is assembled by rigidly securing the nozzle 12 to the casing 24 with bolts, by welding, or other conventional means (not shown). The nozzle insert 18 is then seated in the passage 14 and the element 34 positioned in the chamber. Finally, end closure 26 is rigidly secured to the remainder of the casing by conventional means such as bolts (not shown) and the like.

In the assembled rocket motor 10, as shown in FIG- URE 2, the distance from wall 32 to wall 27 is at least substantially equal to and, preferably, less than the overall length of the element at the lowest temperature at which the motor is to operate. 11f less, the resilient members will be in abutting, compressed relationship with the chamber walls. At higher temperatures, thermal expansion insures that the resilient members remain in abutting, compressed relationship with these walls.

As shown in FIGURE 3, when member 44 is in surface-to-surface compressed relationship with the rear wall 3 2, a seal is formed between the member and the wall which prevents gas from entering the space 56 between the casing and the lateral surface of the element.

The side 58 of member 44 preferably should adhere to both the end 62 of the inhibitor coating and end 60 of the grain. In particular, the ends of the inhibitor coating and the side of the resilient member should adhere tenaciously to each other so that a seal is formed to prevent gases from entering into space 56. It is not essential that the end of the grain adhere to the resilient member although a stronger over-all element is achieved.

The end-Wise cross-sectional dimensions of the member are normally equal to or slightly larger than the endwise cross-sectional dimensions of the element at the point where they are joined. For example, in FIGURE 2 the outside diameter of resilient members 44 and 46 is preferably equal to or slightly larger than that of the inhibited grain although the members may have cross-sectional dimensions smaller than those of the element and still function satisfactorily.

The thickness of the member is not critical though a thicker member can generally withstand greater compression for a longer time without setting. But it also occupies more volume and reduces the amount of fuel which can be loaded into the chamber. The weight of the inhibited grain should be considered as heavier grains may require thicker members. The most satisfactory thickness will depend on the particular conditions. For example, smaller inhibited rocket propellant grains of up to about twelve inches in length and about four inches in diameter may use resilient members of about one eighth inch to about one-half inch in thickness while larger grains will require members of about one-half inch or more in thickness.

The element also can provide the means for holding the nozzle insert in the nozzle passage. As shown in FIGURE 3, the forward end 19 of the insert 18 terminates substantially even with and adjacent to the rear wall 32 and the forward end 19 of the insert and prevents the insert from sliding out of the passage. Preferably, the resilient member will abut against the insert in a compressed relationship to insure that end 20 of the insert is seated against the nozzle flange 16. Obviously the end of the insert and the resilient member can form a gastight seal like the seal formed between the chamber wall and the member. It is not essential that the forward end of the insert and the rear chamber wall terminate in substantially even relationship since the shape of the resilient member can be adapted to engage the end of the insert even if it does not reach the rear chamber wall or if it extends somewhat beyond the rear chamber wall. In operation, the generated gases will maintain the insert properly positioned, even if that portion of the member abutting the insert erodes or burns.

The purpose of the groove is also illustrated in FIG- U-R E 3. Most resilient members tend to set. That is 75 ly one Opening or perforation is present it ordinarily exif the member is maintained in a compressed state over a long period of time and then allowed to expand, it will not expand to its original size. If the resilient member has an indentation or recess in its exposed surface, preferably a continuous groove such as groove 52, the walls 60 of the groove expand into the groove as the member is compressed. Since the resilient material can expand into the groove, the material itself is not as compacted as it would be without the grooves and resists setting.

FIGURE 4 is an end view of rocket motor 10 with end closure 26 of FIGURE 2 removed. Resilient member 46 is part-1y cut-away to expose the various relationships of the components of the motor.

. FIGURES 5 and 6 illustrate other satisfactory resilient members. FIGURE 5 shows a resilient disk having a plurality of rectangular recesses 72 disposed in the exposed surface. A disk of this type would be used on the forward end of the element while a similar disk having a passage through it could be used at either end. Member 74 of FIGURE 6 has a curved, exposed surface with a plurality of circular recesses 76 and a passage 78. This disk can be used at either end of a gas-generating element. Without the passage, it could be used only at the forward end.

It is not essential that these spaces be in the form of recesses in the exposed'surface since hollow spaces inside the member would be useful. However, due to economy of fabrication and other reasons, the surface recesses, particularly continuous grooves, are preferred. The grooves can be U-shaped, V-shaped, or have other de sired configurations, and there can be one or a plurality of grooves. The recesses are not necessary if there is no problem of setting.

The casing and nozzle may be fabricated from a single piece of material, eliminating the need for securing the nozzle to the casing. Conventional materials such as metals and wound glass can be used. If desired the casing and nozzle can be provided with an insulating lining or the nozzle may have an insert made from pyrolytic graphite or other materials having similar properties. Obviously, a gas-generating device does not require a nozzle and, if a nozzle is used, a nozzle insert is not necessary.

Since the resilient members prevent gases from entering the space between the chamber wall and the element, thus preventing overheating of the casing, the present invention permits fabrication of the chamber and nozzle from aluminum, aluminum alloys, and similar metals having relatively low heat resistance. In addition to being lightweight and inexpensive, these metals are easy to machine and resist atmospheric corrosion. A preferred embodiment of the invention comprises a rocket motor of the type shown in FIGURE 2 wherein the nozzle 12 and the casing 24 are fabricated from a single piece of aluminum or an aluminum alloy.

Any of the conventional gas-generated solid compositions and inhibitor coatings are useful in the present invention. Specific examples of suitable propellant compositions are disclosed in U.S. Patents 2,966,403, 2,982,- 638, 2,997,376, 3,028,271, 3,031,347, 2,102,834, and

3,107,186. A variety of inhibitor materials and a meth od'for applying these inhibitors is disclosedin applicants copending application, Serial Number 393,589 filed September 1, 1964. Preferably the inhibitor will be reinforced with a porous sheet such as a woven fabric embedded in the coating and forming an integral part thereof. Particularly preferred reinforced coatings are described in detail in U.S. Patent 3,108,433.

The grain can be completely solid or it may have one or more openings disposed therein along the longitudinal axis to increase the burning surface. The opening can be of any desired shape and extend through the entire length of the grain or only part of this length. Those openings which pass from end to end through the grain are referred to herein as internal perforations. When tends symmetrically along and concentrically with the longitudinal axis. If a plurality of openings is used, they are generally positioned substantially parallel to and symmetrical with the longitudinal axis.

The resilient members can be fabricated from any heatresistant, resilient material. Selection of a particular material will depend on many factors such as the environmental temperatures in which the gas-generating device is to be stored, cycled, and eventually operated; the operating temperature within the combustion chamber; the duration of gas generation, and the intended use of the device. As the natural and synthetic rubbers are very poor thermal conductors and as the operating time of a gas-generator is usually very limited, almost any of these rubbers can be used to fabricate resilient members, particularly for gas-generating devices which produce large quantities of relatively low-temperature gas.

The preferred materials for making the resilient members are the resilient silicone rubber-s. These rubbers are Well-recognized in the art and have been used extensively for making gaskets and the like. They are readily available commercially under various trademarks such as Silastic (Dow Corning Corp). Many silicone rubbers can withstand temperatures ranging from 100 F. to 600 F. before losing their resilient properties.

The resilient members are attached to the ends of the inhibitor and/or the grain with a suitable heat-resistant adhesive. Many well-known adhesives are available for attaching rubber to plastics and other materials. The epoxy adhesives are a particularly suitable class of adhesives for this purpose.

Many obvious modifications of the invention will be apparent to those skilled in the art. Therefore, no undue limitations should be attributed to the invention as a result of the above detailed description except as reflected in the appended claims.

I claim:

1. A gas-generating element comprising, in combination, a solid gas-generating grain and aheat-resistant, resilient member abutting against each end of said grain, one of said members having a passage extending therethrough from side to side thereof and one of said members having a recess disposed in the exposed side surface thereof.

2. A gas-generating element as defined in claim 1 wherein said members are bonded to the ends of said grain in intimate, fixed relationship therewith.

3. A gas-generating element as defined in claim 1 including a coating of inhibitor material in intimate relationship with the external lateral surface of said grain and wherein said members are bonded in intimate, fixed relationship with the ends of said coating.

4. A gas-generating element as defined in claim 1 wherein one of said members has a plurality of recesses in the exposed side surface thereof.

5. A gas-generating device comprising (a) a casing having a chamber therein and a restricted exhaust port in one end thereof, and

(b) a gas-generating element as defined in claim 1 positioned in said chamber with one of said members abutting in compressed relationship against the forward wall of said chamber and the other resilient member abutting in compressed relationship against the rear wall of said chamber, effecting a gas-sealing relationship between said members and said rear and forward walls and between said members and said grain, the resilient member bearing against said rear wall having a passage from side to side therethrough in communication with said port, the distance between the rear wall and the forward wall being less than the length of said element from the exposed side surface of one resilient member to the exposed side surface of the other resilient member at the lowest ambient temperature in which the device is intended to operate.

6. A gas-generating element as defined in claim 5 wherein said members are bonded to the ends of said grain in intimate, fixed relationship therewith.

7. A gas-generating element as defined in claim 5 including a coating of inhibitor material in intimate relationship with the external lateral surface of said grain and wherein said members are bonded in intimate, fixed relationship with the ends of said coating.

8. A gas-generating element as defined in claim 5 wherein one of said members has a plurality of recesses in the exposed side surface thereof.

9. The element according to claim 1 wherein said recess is in the form of a continuous groove spaced from the center and outer edge of the resilient member.

10. The device according to claim 5 having a nozzle, said nozzle being in rigid relationship with said device and having a nozzle passage in communication with said port.

11. The device according to claim 5 wherein said grain has an internal perforation passing from end to end therethrough, said perforation being in communication with the passage in said at least one disk.

References Cited by the Examiner UNITED STATES PATENTS 2,498,080 2/1950 Iasse.

2,876,620 3/1959 Weinland et a]. 35.6 2,956,401 10/1960 Kane 6035.6 2,990,684 7/1961 Cohen 60-35.6

MARK NEWMAN, Primary Examiner.

CARLTON R. CROYLE, Examiner. 

1. A GAS-GENERATING ELEMENT COMPRISING, IN COMBINATION, A SOLID GAS-GENERATING GRAIN AND A HEAT-RESISTANT, RESILIENT MEMBER ABUTTING AGAINST EACH END OF SAID GRAIN, ONE OF SAID MEMBERS HAVING A PASSAGE EXTENDING THERETHROUGH FROM SIDE TO SIDE THEREOF AND ONE OF SAID MEMBERS HAVING A RECESS DISPOSED IN THE EXPOSED SIDE SURFACE THEREOF. 